Heat exchanger

ABSTRACT

A heat exchanger comprising a plurality of heat transfer tubes adapted to transport heat transfer fluid from an inlet to an outlet, the heat transfer tubes comprising elongate hollow members adapted to receive the heat transfer fluid therein, the heat exchanger adapted to receive a flow of heat removal fluid flow between the heat transfer tubes, wherein the heat transfer tubes are arranged such that the heat removal fluid is caused to follow a substantially undulating path through the heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Patent Application No. 61/315,559 filed 19 Mar. 2010, entitled “Heat Exchanger” and which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to a heat exchanger. In particular, it relates to a radiator for cooling a power plant or engine, such as a train engine, and more particularly to a finless radiator for cooling an engine.

BACKGROUND

A heat exchanger that is used to cool a vehicle engine is typically called a radiator. A heat transfer fluid is passed through the engine to absorb the heat generated by the engine. The heated transfer fluid is then passed through radiator tubes within the radiator, which transfers the heat of the heat transfer fluid to a heat removal fluid. The heat removal fluid is usually atmospheric air, which flows over the radiator tubes and absorbs the heat from the heat transfer fluid flowing therein and dissipates it to atmosphere. The air may be forced over the radiator by a fan or the radiator is moved through the air by the vehicle on which it is located.

The amount of heat transferred to the atmosphere by a radiator is related to the surface area exposed to the atmosphere. In general, the greater the surface area, the more heat can be transferred from the heat transfer fluid to the atmosphere. It is common for radiators to include fins mounted on the radiator tubes that convey the fluid through the radiator. The fins greatly increase the surface area of the tubes, enabling more atmospheric air to come into contact with the tube to absorb the heat of the heat transfer fluid. FIG. 2 shows a prior art radiator design. The radiator 20 comprises an inlet 21 and an outlet 22, which are connected by a plurality of spaced tubes 23 a, 23 b, 23 c, 23 d and 23 e. Air acts as the heat removal fluid and flow between the tubes (i.e. into the page) aids the removal of heat from the radiator. Fins 24 extend between the tubes in the form of a zigzagging mesh. The fins 24 receive heat from the tubes 23 a, 23 b, 23 c, 23 d and 23 e by conduction and their large surface area increases the amount of air that comes into contact with the radiator 20 to cool the heat transfer fluid.

It is common for radiators to become blocked with debris. The air flowing over the radiator brings with it insects, plant material, foreign matter and dust, for example. This debris can adhere to the radiator tubes 23 a-e and, in particular, the radiator fins 24. The debris can therefore prevent the flow of air over and between the fins which reduces the cooling efficiency of the radiator. This can be a significant problem for train engines or other power plants, which generate a lot of heat and require efficient cooling in a limited space. It is common for train engines to overheat because the radiator has become so clogged that it cannot maintain a sufficient rate of cooling. This can lead to delays because trains will need to slow or stop to cool down. In more extreme cases, the engine may breakdown due to heat damage.

It is also very difficult to clean the radiator to clear the debris from the radiator fins. There are typically hundreds of fins having small gaps between them which make cleaning time consuming and difficult. Further, jet washing the radiator can often push debris further within the radiator, making it even more difficult to extract.

BRIEF SUMMARY OF THE INVENTION

According to the invention, we provide a heat exchanger comprising a plurality of heat transfer tubes adapted to transport heat transfer fluid from an inlet to an outlet. The heat transfer tubes comprise elongate hollow members adapted to receive the heat transfer fluid therein. The heat exchanger is adapted to receive a flow of heat removal fluid flow between the heat transfer tubes. The heat transfer tubes are arranged such that the heat removal fluid is caused to follow a substantially undulating path through the heat exchanger.

This is advantageous as the arrangement of heat transfer tubes promotes efficient heat transfer to the heat removal fluid without the need for fins. The undulating path followed by the heat removal fluid results in increased contact between the fluid and the heat transfer tubes and also promotes turbulence within the heat exchanger. It has been found that this arrangement is sufficiently efficient to obviate the need for fins. The heat transfer tubes can be substantially smooth and shaped to cause the heat removal fluid to follow the undulating path. As the undulating path is provided by the shape or arrangement of the walls of the heat transfer tubes rather than by any fins or projections, the heat transfer tubes gather little dirt and debris and are easily cleaned.

Preferably, the heat exchanger comprises a first stack of heat transfer tubes and a second stack of heat transfer tubes, each heat transfer tube having at least one director surface, the heat transfer tubes of each stack being spaced apart and adapted to receive the flow of heat removal fluid over their director surface and therebetween, the stacks including an intake side and an exhaust side, the stacks being arranged such that, in use, the heat removal fluid is received through the intake side and exhausted through the exhaust side, the exhaust side of the first stack arranged adjacent the intake side of the second stack, wherein the director surfaces of the heat transfer tubes in the second stack are inclined at a different angle to the director surfaces of the heat transfer tubes in the first stack.

Thus, the director surfaces of each stack or row are arranged to change the direction of the flow of the heat removal fluid, which promotes heat transfer to the heat removal fluid. This is thought to be due to the creation of turbulence between the heat transfer tubes and between the stacks or rows, which improves the contact of the heat removal fluid with the heat transfer tubes and therefore enhances the transfer of heat between the heat transfer fluid and the heat removal fluid. As the heat exchanger does not require fins, it is significantly more reliable, as debris cannot collect within the radiator thus maintaining a good flow of heat removal fluid. It is also easy to clean.

Preferably, the heat exchanger includes a further stack of heat transfer tubes, the stacks of heat transfer tubes being arranged such that the heat removal fluid flows first through the first stack, then the second stack and then each further stack, the inclination of the director surfaces of the further stack arranged to be at a different angle to the director surfaces of a preceding stack.

Preferably the director surface of the heat transfer tubes in each stack is inclined to the average direction of flow of heat removal fluid received at the intake side. This is advantageous as the director surfaces will disrupt the air flow from its flow path. In particular, a fan will typically draw heat removal fluid in a direction perpendicular to the plane of the stacks and the director surfaces will successively alter the flow from this directional path as it flows through the heat exchanger.

In particular, the director surfaces of the first stack of heat transfer tubes may be arranged to be inclined at a positive angle to the average direction of flow of heat removal fluid through the heat exchanger and the director surfaces of the second stack of heat transfer tubes are arranged to be inclined at a negative angle to the average direction of flow of heat removal fluid.

In particular, the inclination of the director surfaces and the arrangement of the stacks are preferably such that a tangent to the director surface of a tube in the first stack falls upon the director surface of a tube in an adjacent stack. This helps promote the undulating flow path through the heat exchanger and therefore the turbulance.

Preferably the heat exchanger is a finless radiator.

There now follows, by way of example only, a detailed description of the invention with reference to the following drawings, in which;

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a heat exchanger in accordance with the invention;

FIG. 2 shows a prior art radiator design;

FIG. 3 shows four stacks of heat transfer tubes in cross-section;

FIG. 4 shows a close-up of a part of FIG. 3;

FIG. 5 shows the internal structure of a heat transfer tube; and

FIG. 6 shows a further embodiment of a heat exchanger in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The heat exchanger of the embodiment shown in FIG. 1 is specifically a radiator 1 for cooling a train diesel engine. A heat transfer fluid, which in this embodiment is a water based coolant, is pumped through the engine to absorb the heat generated thereby. The radiator 1 is mounted at the side of the train perpendicular to the direction of travel. A fan is used to cause atmospheric air, which is the heat removal fluid, to flow through the radiator to remove the heat to atmosphere.

The radiator 1 comprises an inlet 2 to receive the coolant from the engine. An outlet 3 returns the coolant, once cooled by its passage through the radiator 1, to the engine water jackets and pipework for recirculation. The radiator 1 includes a plurality of heat transfer tubes 4 that connect the inlet 2 and outlet 3. Thus, the coolant received at the inlet 2 passes through a distributor or inlet header, which distributes the coolant into the heat transfer tubes 4. The coolant flows through the heat transfer tubes 4 and is directed into the outlet 3 by a further distributor or outlet header.

The heat transfer tubes 4 comprise elongate hollow slats and are best shown in FIG. 4. The slats 4 have a narrow leading edge 5 and a narrow trailing edge 6, separated by a wider first side 7 and wider second side 8. The first side 7 and the second side 8 act as director surfaces 9. Thus, the director surface is adjacent the leading edge and faces the incoming heat removal fluid flow. The director surfaces 9 are substantially flat and smooth. Thus, it is the outer wall of the tube that provides the smooth director surface 9 rather than any fins or projections. The leading edge 5, and perhaps the trailing edge 6, are rounded to provide a smooth transition into the first and second sides 7, 8.

FIG. 3 shows the radiator 1 of FIG. 1 in cross-section. The heat transfer tubes 4 are spaced apart and arranged wider side 7, 8 by wider side 7, 8 to form a stack 10. The stacks 10 are arranged together to form a matrix. The heat transfer tubes 4 are finless and are therefore not connected by fins. The radiator of this embodiment includes four stacks of heat transfer tubes 4, with each stack comprising forty seven heat transfer tubes 4. The first stack is labelled 10 a, the second stack is labelled 10 b, the third stack is labelled 10 c and the fourth stack is labelled 10 d. Each of the stacks includes an intake side 11 and an exhaust side 12. Air is received at the intake side 11, adjacent the leading edges 5, and leaves the stack 10 at an exhaust side 12, adjacent the trailing edges 6. The intake side 11 of the second stack 10 b is located adjacent the exhaust side 12 of the first stack 10 a. The intake side 11 of the third stack 10 c is located adjacent the exhaust side 12 of the second stack 10 b. The intake side 11 of the fourth stack 10 d is located adjacent the exhaust side 12 of the third stack 10 c. The fan of the radiator 1 draws or forces heat removal fluid to flow through the radiator from the intake side 11 of the first stack 10 a to the exhaust side 12 of the fourth stack 10 d. The average direction of flow of the heat removal air is shown by arrows A. The air flows through the radiator 1 between the heat transfer tubes 4 of the first stack, then between the tubes 4 of the subsequent stacks, following an undulating path as it does so.

FIG. 4 shows a close up of the stacks 10 a, 10 b, 10 c and 10 d. The heat transfer tubes 4 of the first stack 10 a and, in particular, the director surfaces 9 are inclined to the average direction of the incoming air arriving at the intake side 11. In the stack arrangement of this embodiment, the heat transfer tubes 4 are also inclined to a normal of the plane in which the stack lies. Dashed lines in FIG. 4 shows how the director surfaces 9 of the heat transfer tubes 4 in the first stack 10 a are inclined to the heat removal air flow or the normal to the plane in which the radiator is mounted by an angle of −θ°. The director surfaces 9 of the heat transfer tubes 4 of the second stack 10 b are also inclined, but at an angle of +θ°. Thus, the director surfaces 9 of the second stack 10 b are inclined at a different angle to the director surfaces 9 of the first stack 10 a. The director surfaces 9 of the heat transfer tubes 4 of the third stack 10 c are also inclined, but at an angle of −θ°. Thus, the director surfaces 9 of the third stack 10 c are inclined at a different angle to the director surfaces 9 of the preceding second stack 10 b. Similarly, the director surfaces 9 of the heat transfer tubes 4 of the fourth stack 10 d are also inclined, but at an angle of +θ°.

Thus, the director surfaces 9 of the fourth stack 10 d are inclined at a different angle to the director surfaces 9 of the preceding third stack 10 c. It will be appreciated that the degree of inclination need not be the same between stacks nor within a single stack.

This arrangement results in an undulating path being formed by the alternately inclined director surfaces 9 of the stacks 10 a, 10 b, 10 c and 10 d. The dashed arrows 13 show, in general, the undulating path followed by the air flow between the heat transfer tubes. Thus, the air arriving at the first stack is directed upwards (as shown in the Figure) primarily by the director surface 9 of the first side 7 of the heat transfer tubes in the first stack 10 a. Air leaving the exhaust side 12 of the first stack is then directed downwardly primarily by the director surface 9 of the second side 8 of the heat transfer tubes in the second stack 10 b. Similarly, the director surfaces 9 of the third and fourth stacks 10 c, 10 d direct the air upwardly and downwardly respectively. In particular the inclination of the director surfaces 9 and the arrangement of the stacks 10 a, 10 b, 10 c, 10 d are such that a tangent to the director surface 9 of a tube 4 in the first stack falls upon the director surface of a tube in an adjacent stack. Thus, the tangent 14 of director surface 9 in the third stack 10 c falls upon the director surface 9 of a tube in the fourth stack 10 d.

This arrangement improves heat removal from the tubes 4 to the air. In particular, as the director surfaces 9 change the direction of the air flow, contact between the air and the heat transfer tubes is improved as air is forced against the tubes 4. Also, as there are no fins extending between the tubes 4, more air can flow through the radiator 4. Turbulence and eddies are generated between the stacks 10 a, 10 b, 10 c, 10 d due to the director surfaces disrupting the flow, which is thought to improve contact between the air and the tubes 4. Thus, the radiator 1 can operate efficiently and is also resistant to clogging due to the lack of fins and is easy to keep clean. This improves the reliability of the diesel engine to which the radiator 1 is attached. Thus, shaping the heat transfer tubes 4 by way of the substantially smooth, projection free, outer wall of the tube to encourage the air to follow an undulating path has been found to be surprisingly effective.

FIG. 5 shows the internal structure of the heat transfer slats 4. The hollow slat is divided into a plurality of sub-channels 15 by internal divider walls 16. Within each of the sub-channels 15, ridge portions 17 extend inwardly from the first wall 7 and second wall 8. In particular, a first ridge portion 18 extends from the first wall 7 and a second ridge portion 19 extends from the second wall 8. The walls and ridges increase the internal surface area of the tube/slat 4.

FIG. 6 shows a further embodiment of the radiator 1. The same reference numerals have been used to designate like parts. In this embodiment, the heat transfer tubes 4 comprise elongate members having a V-shaped cross-section. The elongate members have a single leading edge 5 and two trailing edges 6 a and 6 b. The heat transfer tubes 4 are arranged in stacks, but the tubes 4 of an adjacent stack in this embodiment are substantially aligned with the gaps between the tubes 4 of the other stack. This arrangement defines an undulating path as shown in general by dashed arrow 60.

Each heat transfer tube 4 has two director surfaces 9. In particular, a first director surface 61 and a second director surface 62. The first director surface 61 of each tube is inclined at a negative angle −θ to the average direction of incoming air, while the second director surface 62 of each tube is inclined at a positive angle +θ to the average direction of incoming air. Therefore, as in the previous embodiment, air entering the intake side 11 is diverted from its flow path by the director surfaces 61 and 62 generally towards the director surfaces 61 and 62 of the tubes in the subsequent stack. The change of direction of the air flow at each stack aids in the transfer of heat from the tubes 4 to the air. Therefore the inclination of the director surfaces and the arrangement of the stacks are such that a tangent to the director surface of a tube in the first stack falls upon the director surface of a tube in an adjacent stack. Thus, the tangent 64 of director surface 62 in stack 10 a falls upon the director surface 61 of a tube in the stack 10 b.

Further, in the present embodiment, turbulence and eddies are formed adjacent the recessed backs 63 of the tubes 4. This is thought to further enhance heat transfer.

It will be appreciated that while an arrangement comprising four stacks has been described, other numbers of stacks could be used. Further, the number of tubes within a stack may differ. The number of tubes that make up a stack may also differ between stacks that make up a single radiator. Also, the radiator may be adapted for use with other power plants, such as petrol engines.

The heat removal fluid could be a heat introduction fluid and wherein the radiator is arranged to take heat from the heat introduction fluid and transfer it to the heat transfer fluid. 

1. A heat exchanger comprising a plurality of heat transfer tubes adapted to transport heat transfer fluid from an inlet to an outlet, the heat transfer tubes comprising smooth elongate hollow members adapted to receive the heat transfer fluid therein, the heat exchanger adapted to receive a flow of heat removal fluid flow between the heat transfer tubes, wherein the heat transfer tubes are arranged such that the heat removal fluid is caused to follow a substantially undulating path through the heat exchanger.
 2. A heat exchanger in accordance with claim 1, in which each of the heat transfer tubes are defined by an outer wall, at least part of the outer wall being substantially flat and smooth and defining a director surface, the director surface arranged to direct the heat removal fluid to follow the substantially undulating path through the heat exchanger.
 3. A heat exchanger in accordance with claim 1, in which the heat exchanger comprises a first stack of heat transfer tubes and a second stack of heat transfer tubes, each heat transfer tube having at least one director surface, the heat transfer tubes of each stack being spaced apart and adapted to receive the flow of heat removal fluid over their director surface and therebetween, the stacks including an intake side and an exhaust side, the stacks being arranged such that, in use, the heat removal fluid is received through the intake side and exhausted through the exhaust side, the exhaust side of the first stack arranged adjacent the intake side of the second stack, wherein the director surfaces of the heat transfer tubes in the second stack are inclined at a different angle to the director surfaces of the heat transfer tubes in the first stack.
 4. A heat exchanger in accordance with claim 3, in which the heat exchanger includes a further stack of heat transfer tubes, the stacks of heat transfer tubes being arranged such that the heat removal fluid flows first through the first stack, then the second stack and then each further stack, the inclination of the director surfaces of each further stack arranged to be at a different angle to the director surfaces of a preceding stack.
 5. A heat exchanger in accordance with claim 3, in which the director surface of the heat transfer tubes in each stack is inclined to the average direction of flow of heat removal fluid received at the intake side.
 6. A heat exchanger in accordance with claim 5, in which the director surfaces of the first stack of heat transfer tubes are arranged to be inclined at a positive angle to the average direction of flow of heat removal fluid through the heat exchanger and the director surfaces of the second stack of heat transfer tubes are arranged to be inclined at a negative angle to the average direction of flow of heat removal fluid.
 7. A heat exchanger in accordance with claim 3, in which the inclination of the director surfaces and the arrangement of the stacks are such that a tangent to the director surface of a tube in the first stack falls upon the director surface of a tube in an adjacent stack.
 8. A heat exchanger in accordance with claim 1, in which the heat exchanger is a finless radiator.
 9. A heat exchanger in accordance with claim 1, in which the heat transfer tubes comprise hollow slats.
 10. A heat exchanger in accordance with claim 9, in which the slats are substantially flat on their external surface.
 11. A heat exchanger in accordance with claim 9, in which each of the heat transfer tubes are defined by an outer wall, at least part of the outer wall being substantially flat and smooth and defining a director surface, the director surface arranged to direct the heat removal fluid to follow the substantially undulating path through the heat exchanger and wherein the slats comprise two opposed edges separated by two wider sides, the director surface being provided by one of the wider sides. 